Park tool chain checker cc2to alleviate poor shifting and uneven drivetrain wear most manufacturers recommend chain replacement at or before 075 stretch now you can quickly and accurately determine the wear and stretch of any chain with the park tool chain checker featuressimply insert the chain checkers pins into two links press the swing arm gauge tight and then check the gauge window for an accurate readingreads wear from 025 to 1 91011 speed compatible 910 speed chains repla